Non-contact power supply apparatus, program, method for controlling non-contact power supply apparatus, and non-contact power transmission system

ABSTRACT

A control circuit controls a plurality of conversion switching elements by first drive signals and a plurality of adjustment switching elements by second drive signals. The control circuit is configured to adjust a phase difference which is a delay of the phase of each of the second drive signals to the phase of each of the first drive signals to a set value within a prescribed range to adjust the magnitude of output power. The prescribed range includes at least one of a range of 270 degrees to 360 degrees and a range of 90 degrees to 180 degrees.

TECHNICAL FIELD

The present invention generally relates to non-contact power supplyapparatuses, programs, methods for controlling the non-contact powersupply apparatuses, and non-contact power transmission systems. Morespecifically, the present invention relates to a non-contact powersupply apparatus, a program, a method for controlling the non-contactpower supply apparatus, and a non-contact power transmission system thatare for supplying power to a load in a non-contact manner.

BACKGROUND ART

A non-contact power supply apparatus configured to supply power to aload by using electromagnetic induction in a non-contact manner has beenproposed (e.g., see Patent Literature 1).

The non-contact power supply apparatus described in Patent Literature 1includes a primary coil (power feeding coil) configured to generate amagnetic field to supply electric power and is used to feed power to amobile object such as an electric car. The electric car includes anon-contact power reception apparatus. The non-contact power receptionapparatus includes a secondary coil (power receiving coil) and a storagebattery and accumulates electric power supplied from the primary coil ofthe non-contact power supply apparatus to the secondary coil in thestorage battery.

However, in such a non-contact power supply apparatus, the couplingcoefficient between the primary coil and the secondary coil changesdepending on the relative positional relationship between the primarycoil of the non-contact power supply apparatus and the secondary coil ofthe load (mobile object). Thus, when the relative positionalrelationship between the primary coil and the secondary coil changes,output power output from the non-contact power supply apparatusdecreases, and the output power may be smaller than required electricpower.

CITATION LIST Patent Literature

Patent Literature 1: JP 2013-243929 A

SUMMARY OF INVENTION

In view of the above problems, it is an object of the present inventionto provide a non-contact power supply apparatus, a program, a method forcontrolling the non-contact power supply apparatus, and a non-contactpower transmission system which easily secure required electric powereven when the relative positional relationship between a primary coiland a secondary coil changes.

A non-contact power supply apparatus according to one aspect of thepresent invention includes an inverter circuit, a primary coil, avariable capacitance circuit, and a control circuit. The invertercircuit includes a plurality of conversion switching elementselectrically connected between a pair of input points and a pair ofoutput points. The inverter circuit is configured to convert adirect-current voltage applied to the pair of input points into analternating-current voltage by switching the plurality of conversionswitching elements and to output the alternating-current voltage fromthe pair of output points. The primary coil is electrically connectedbetween the output points in the pair and is configured to supply outputpower to a secondary coil in a non-contact manner when thealternating-current voltage is applied to the primary coil. The variablecapacitance circuit is electrically connected between the pair of outputpoints and the primary coil. The variable capacitance circuit includesan adjustment capacitor and a plurality of adjustment switchingelements. The variable capacitance circuit is configured to adjust amagnitude of a capacity component between the pair of output points andthe primary coil by switching the plurality of adjustment switchingelements. The control circuit is configured to control the plurality ofconversion switching elements by a first drive signal and to control theplurality of adjustment switching elements by a second drive signal. Thecontrol circuit is configured to adjust a phase difference which is adelay of a phase of the second drive signal to a phase of the firstdrive signal to a set value within a prescribed range to adjust amagnitude of the output power. The prescribed range includes at leastone of a range of 270 degrees to 360 degrees and a range of 90 degreesto 180 degrees.

A program according to one aspect of the present invention causes acomputer to function as a controller, wherein the computer is used in anon-contact power supply apparatus. The non-contact power supplyapparatus includes an inverter circuit, a primary coil, and a variablecapacitance circuit. The inverter circuit includes a plurality ofconversion switching elements electrically connected between a pair ofinput points and a pair of output points. The inverter circuit isconfigured to convert a direct-current voltage applied to the pair ofinput points into an alternating-current voltage by switching theplurality of conversion switching elements and to output thealternating-current voltage from the pair of output points. The primarycoil is electrically connected between the output points in the pair andis configured to supply output power to a secondary coil in anon-contact manner when the alternating-current voltage is applied tothe primary coil. The variable capacitance circuit is electricallyconnected between the pair of output points and the primary coil. Thevariable capacitance circuit includes an adjustment capacitor and aplurality of adjustment switching elements. The variable capacitancecircuit is configured to adjust the magnitude of a capacity componentbetween the pair of output points and the primary coil by switching theplurality of adjustment switching elements. The controller is configuredto control the plurality of conversion switching elements by a firstdrive signal and to control the plurality of adjustment switchingelements by a second drive signal. The controller is configured toadjust a phase difference which is a delay of a phase of the seconddrive signal to a phase of the first drive signal to a set value withina prescribed range including at least one of a range of 270 degrees to360 degrees and a range of 90 degrees to 180 degrees to adjust amagnitude of the output power.

A method for controlling a non-contact power supply apparatus accordingto one aspect of the present invention includes: controlling a pluralityof conversion switching elements by a first drive signal; andcontrolling a plurality of adjustment switching elements by a seconddrive signal. The non-contact power supply apparatus includes aninverter circuit, a primary coil, and a variable capacitance circuit.The inverter circuit includes a plurality of conversion switchingelements electrically connected between a pair of input points and apair of output points. The inverter circuit is configured to convert adirect-current voltage applied to the pair of input points into analternating-current voltage by switching the plurality of conversionswitching elements and to output the alternating-current voltage fromthe pair of output points. The primary coil is electrically connectedbetween the output points in the pair and is configured to supply outputpower to a secondary coil in a non-contact manner when thealternating-current voltage is applied to the primary coil. The variablecapacitance circuit is electrically connected between the pair of outputpoints and the primary coil. The variable capacitance circuit includesan adjustment capacitor and a plurality of adjustment switchingelements. The variable capacitance circuit is configured to adjust amagnitude of a capacity component between the pair of output points andthe primary coil by switching the plurality of adjustment switchingelements. The method for controlling the non-contact power supplyapparatus includes adjusting a phase difference which is a delay of aphase of the second drive signal to a phase of the first drive signal toa set value within a prescribed range including at least one of a rangeof 270 degrees to 360 degrees and a range of 90 degrees to 180 degreesto adjust a magnitude of the output power.

A non-contact power transmission system according to one aspect of thepresent invention includes the non-contact power supply apparatus and anon-contact power reception apparatus including the secondary coil. Thenon-contact power reception apparatus is configured to be supplied withthe output power from the non-contact power supply apparatus in anon-contact manner.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a circuit diagram illustrating a non-contact powertransmission system according to an embodiment of the present invention;

FIG. 2 is a waveform diagram illustrating first drive signals and seconddrive signals of a non-contact power supply apparatus according to theembodiment of the present invention:

FIG. 3 is a graph illustrating an example of resonance characteristicsof the non-contact power supply apparatus;

FIGS. 4A and 4B are graphs illustrating examples of resonancecharacteristics of the non-contact power supply apparatus;

FIG. 5A is a graph illustrating an example of phase differencecharacteristics in the case of an initial leading phase of thenon-contact power supply apparatus, and FIG. 5B is a graph illustratingan example of phase difference characteristics in the case of an initiallagging phase of the non-contact power supply apparatus;

FIG. 6A is an explanatory view illustrating a first charge mode of avariable capacitance circuit in the non-contact power supply apparatus,FIG. 6B is an explanatory view illustrating a first discharge mode ofthe variable capacitance circuit in the non-contact power supplyapparatus, FIG. 6C is an explanatory view illustrating a second chargemode of the variable capacitance circuit in the non-contact power supplyapparatus, and FIG. 6D is an explanatory view illustrating a seconddischarge mode of the variable capacitance circuit in the non-contactpower supply apparatus;

FIG. 7 is a waveform diagram illustrating a first drive signal, aprimary current, and a second drive signal in the case where avoltage-current phase difference in the non-contact power supplyapparatus is 90 degrees;

FIG. 8 is a waveform diagram illustrating the first drive signal, theprimary current, and the second drive signal in the case where thevoltage-current phase difference in the non-contact power supplyapparatus is 45 degrees;

FIG. 9 is a flowchart illustrating output power control in thenon-contact power supply apparatus;

FIG. 10A is a graph illustrating an example of phase difference-coilcurrent characteristics of the non-contact power supply apparatus, andFIG. 10B is an enlarged graph of the area A1 of FIG. 10A;

FIG. 11 is a flowchart illustrating operation of the non-contact powersupply apparatus in a search mode;

FIG. 12 is a graph illustrating an example of resonance characteristicsof the non-contact power supply apparatus; and

FIG. 13 is a circuit diagram illustrating the configuration of avariable capacitance circuit according to a variation according to theembodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

A non-contact power supply apparatus of the present embodiment suppliespower to a load in a non-contact manner. The non-contact power supplyapparatus transfers electric power from a primary coil included in thenon-contact power supply apparatus to a secondary coil included in theload to supply power to the load, with the primary coil and thesecondary coil being in an electromagnetically (at least eitherelectrically or magnetically) coupled state. Such a non-contact powersupply apparatus and a non-contact power reception apparatus included inthe load form a non-contact power transmission system.

<Outline of Non-Contact Power Transmission System>

First, with reference to FIG. 1, an outline of the non-contact powertransmission system will be described.

A non-contact power transmission system 1 includes a non-contact powersupply apparatus 2 including a primary coil L1 and a non-contact powerreception apparatus 3 including a secondary coil L2. The non-contactpower reception apparatus 3 is configured receive output power from thenon-contact power supply apparatus 2 in a non-contact manner. The outputpower here is electric power output from the non-contact power supplyapparatus 2 and supplied from the primary coil L1 to the secondary coilL2 in a non-contact manner when an alternating-current voltage isapplied to the primary coil L1.

In the present embodiment, an example will be described in which thenon-contact power reception apparatus 3 is mounted on an electricvehicle serving as the load. The electric vehicle is a vehicle includinga storage battery 4 and propelled by using electrical energy accumulatedin the storage battery 4. The non-contact power reception apparatus 3mounted on the electric vehicle is used as a charger of the storagebattery 4. Note that while an electric car propelled by using drivingforce generated by an electric motor is described as an example of anelectric vehicle, the electric vehicle is not limited to the electriccar but may be a two-wheel vehicle (electric motorcycle), an electricbicycle, or the like.

The non-contact power supply apparatus 2 supplies electric powersupplied from a power generating facility such as a commercial powersupply (system power supply) or a photovoltaic power generating facilityto the non-contact power reception apparatus 3 to charge the storagebattery 4 of the electric vehicle. Electric power supplied to thenon-contact power supply apparatus 2 may be either alternating-currentpower or direct-current power, but in the present embodiment, a casewhere the non-contact power supply apparatus 2 is electrically connectedto a direct-current power supply 5 and direct-current power is suppliedto the non-contact power supply apparatus 2 will be described as anexample. Note that when alternating-current power is supplied to thenon-contact power supply apparatus 2, the non-contact power supplyapparatus 2 includes an AC/DC converter configured to convert analternating current into a direct current.

The non-contact power supply apparatus 2 is installed in a parking lotof, for example, a commercial facility, a public facility, a multipledwelling house, or the like. At least the primary coil L1 of thenon-contact power supply apparatus 2 is installed on a floor or ground,and the non-contact power supply apparatus 2 supplies electric power tothe non-contact power reception apparatus 3 of an electric vehicleparked above the primary coil L1 in a non-contact manner. Here, thesecondary coil L2 of the non-contact power reception apparatus 3 islocated above the primary coil L1 so as to be electromagnetically (atleast either electrically or magnetically) coupled to the primary coilL1. Thus, the output power from the primary coil L1 is transferred(transmitted) to the secondary coil L2. Note that the primary coil L1does not necessarily have to be installed to be exposed from a floor orground but may be embedded in a floor or ground.

The non-contact power reception apparatus 3 includes the secondary coilL2, a pair of secondary capacitors C21 and C22, a rectifier circuit 31,and a smoothing capacitor C2. The rectifier circuit 31 includes a diodebridge including a pair of alternating-current input points and a pairof direct-current output points. The secondary coil L2 has one endelectrically connected to one of the alternating-current input points ofthe rectifier circuit 31 via the first secondary capacitor C21. Thesecondary coil L2 has the other end electrically connected to the otherof the alternating-current input points of the rectifier circuit 31 viathe second secondary capacitor C22. The smoothing capacitor C2 iselectrically connected between the direct-current output points in thepair in the rectifier circuit 31. Moreover, the smoothing capacitor C2has both ends electrically connected to respective output terminals T21and T22 which are paired. The storage battery 4 is electricallyconnected to the pair of output terminals T21 and T22.

Thus, the non-contact power reception apparatus 3 rectifies by therectifier circuit 31 an alternating-current voltage generated across thesecondary coil L2 by receiving the output power from the primary coil L1of the non-contact power supply apparatus 2 by the secondary coil L2 andfurther smooths the alternating-current voltage by the smoothingcapacitor C2 to obtain a direct-current voltage. The non-contact powerreception apparatus 3 outputs (applies) the thus obtained direct-currentvoltage from the pair of output terminals T21 and T22 to the storagebattery 4.

Here, in the present embodiment, the non-contact power supply apparatus2 includes a variable capacitance circuit 22 and a pair of primarycapacitors C11 and C12. The variable capacitance circuit 22 and theprimary coil L1 form a resonance circuit (hereinafter referred to as a“primary resonance circuit”). Moreover, in the non-contact powerreception apparatus 3, the secondary coil L2 and the pair of secondarycapacitors C21 and C22 form a resonance circuit (hereinafter referred toas a “secondary resonance circuit”). The non-contact power transmissionsystem 1 of the present embodiment adopts a magnetic field resonancemethod (magnetic resonance method) for producing resonance of theprimary resonance circuit with the secondary resonance circuit totransmit electric power. That is, the non-contact power transmissionsystem 1 matches the resonance frequency of the primary resonancecircuit and the resonance frequency of the secondary resonance circuitwith each other to enable highly efficient transmission of the outputpower of the non-contact power supply apparatus 2 even when the primarycoil L1 and the secondary coil L2 are relatively far away from eachother.

<Outline of Non-Contact Power Supply Apparatus>

Next, with reference to FIG. 1, an outline of the non-contact powersupply apparatus will be described.

The non-contact power supply apparatus 2 of the present embodimentfurther includes an inverter circuit 21, the variable capacitancecircuit 22, and a control circuit 23 in addition to the primary coil L1.

The inverter circuit 21 includes a plurality of (here, four) conversionswitching elements Q1 to Q4 electrically connected between a pair ofinput points 211 and 212 and a pair of output points 213 and 214. Theinverter circuit 21 converts a direct-current voltage applied to thepair of input points 211 and 212 into an alternating-current voltage byswitching the plurality of conversion switching elements Q1 to Q4 andoutputs the alternating-current voltage from the pair of output points213 and 214.

The primary coil L1 is electrically connected between the output points213 and 214 in the pair and supplies output power to the secondary coilL2 in a non-contact manner when the alternating-current voltage isapplied to the primary coil L1.

The variable capacitance circuit 22 is electrically connected betweenthe pair of output points 213 and 214 and the primary coil L1 andincludes an adjustment capacitor C1 and a plurality of (heir, four)adjustment switching elements Q5 to Q8. The variable capacitance circuit22 adjusts the magnitude of a capacity component between the pair ofoutput points 213 and 214 and the primary coil L1 by switching theplurality of adjustment switching elements Q5 to Q8.

The control circuit 23 controls the plurality of conversion switchingelements Q1 to Q4 by a first drive signal and controls the plurality ofadjustment switching elements Q5 to Q8 by a second drive signal. Thecontrol circuit 23 is configured to adjust a phase difference which is adelay of a phase of the second drive signal to a phase of the firstdrive signal to a set value within a prescribed range to adjust themagnitude of the output power. The prescribed range is at least one of arange of 270 degrees to 360 degrees and a range of 90 degrees to 180degrees.

The “phase difference” here is a delay of the phase of each of seconddrive signals G6 and G7 to the phase of each of first drive signals G1and G4 or a delay of the phase of each of second drive signals G5 and G8to the phase of each of first drive signals G2 and G3. This point willbe described later in detail in “(2) With Variable Capacitance Circuit”of “Basic Operation.”

With this configuration, the non-contact power supply apparatus 2 of thepresent embodiment provides the advantage that even when the relativepositional relationship between the primary coil L1 and the secondarycoil L2 changes, required electric power is easily secured. That is, thenon-contact power supply apparatus 2 adjusts the phase difference, whichis a delay of the phase of each of the second drive signals G6 and G7(G5 and G8) to the phase of each of the first drive signals G1 and G4(G2 and G3), to the set value within the prescribed range, therebyenabling adjustment of the magnitude of the output power. Thus, even ifa change in the relative positional relationship between the primarycoil L1 and the secondary coil L2 changes the coupling coefficientbetween the primary coil L1 and the secondary coil L2, the non-contactpower supply apparatus 2 easily secures required electric power byadjusting the phase difference. Moreover, since the phase difference isadjusted to the set value within the prescribed range including at leastone of a range of 270 degrees to 360 degrees and a range of 90 degreesto 180 degrees, the inverter circuit 21 is operable in a lagging phasemode when the prescribed range satisfies prescribed conditions. The“lagging phase mode” will be described later in detail in item “LeadingPhase Mode and Lagging Phase Mode.”

Note that the “input point” and the “output point” mentioned in thepresent embodiment do not have to be entities as components (terminals)for connection to electric wires and the like and may be, for example,parts of a lead of an electronic component or a conductor included in acircuit board.

<Circuit Configuration>

Next, with reference to FIG. 1, a specific circuit configuration of thenon-contact power supply apparatus 2 of the present embodiment will bedescribed.

The non-contact power supply apparatus 2 of the present embodimentincludes the pair of input terminals T11 and T12. The direct-currentpower supply 5 is electrically connected to the pair of input terminalsT11 and T12.

The inverter circuit 21 is a full-bridge inverter circuit including afull-bridge connection of the four conversion switching elements Q1 toQ4. That is, the inverter circuit 21 includes a first arm and a secondarm electrically connected in parallel to each other between the inputpoints 211 and 212 in the pair, and the first arm and the second armincludes the four conversion switching elements Q1 to Q4. The first armincludes a series circuit of the (first) conversion switching element Q1and the (second) conversion switching element Q2. The second armincludes a series circuit of the (third) conversion switching element Q3and the (fourth) conversion switching element Q4. A midpoint of thefirst arm (a connection point of the conversion switching elements Q1and Q2) and a midpoint of the second arm (a connection point of theconversion switching elements Q3 and Q4) are respectively the outputpoints 213 and 214 in the pair. In the present embodiment, the fourconversion switching elements Q1 to Q4 are each an n-channel depletionMetal-Oxide-Semiconductor Field-Effect Transistor (MOSFET).

More specifically, the pair of input points 211 and 212 is electricallyconnected to the pair of input terminals T11 and T12 such that the firstinput point 211 is adjacent to the positive electrode of thedirect-current power supply 5 and the second input point 212 is adjacentto the negative electrode of the direct-current power supply 5. Thedrains of the conversion switching elements Q1 and Q3 are electricallyconnected to the first input point 211. The sources of the conversionswitching elements Q2 and Q4 are electrically connected to the secondinput point 212. A connection point of the source of the conversionswitching element Q1 and the drain of the conversion switching elementQ2 is the first output point 213 of the inverter circuit 21. Aconnection point of the source of the conversion switching element Q3and the drain of the conversion switching element Q4 is the secondoutput point 214 of the inverter circuit 21.

The four conversion switching elements Q1 to Q4 are electricallyconnected to four diodes D1 to D4 respectively. The diode D1 iselectrically connected between the drain and the source of theconversion switching element Q1. The diode D2 is electrically connectedbetween the drain and the source of the conversion switching element Q2.The diode D3 is electrically connected between the drain and the sourceof the conversion switching element Q3. The diode D4 is electricallyconnected between the drain and the source of the conversion switchingelement Q4. The diodes D1 the D4 are connected to the conversionswitching elements Q1 to Q4 in such an orientation that the cathodes ofthe diodes D1 to D4 are adjacent to the drains of the conversionswitching elements Q1 to Q4, respectively. Here, the diodes D1 to D4 areparasitic diodes of the conversion switching elements Q1 to Q4,respectively.

The variable capacitance circuit 22 includes the adjustment capacitor C1and the four adjustment switching elements Q5 to Q8. The variablecapacitance circuit 22 includes a third arm and a fourth arm which areelectrically connected in parallel to each other between the outputpoints 213 and 214 in the pair in the inverter circuit 21. The third armand the fourth arm include the four adjustment switching elements Q5 toQ8. The third arm includes a series circuit of the (first) adjustmentswitching element Q5 and the (third) adjustment switching element Q7.The fourth arm includes a series circuit of the (second) adjustmentswitching element Q6 and the (fourth) adjustment switching element Q8.The adjustment capacitor C1 is electrically connected between a midpointof the third arm (a connection point of the adjustment switchingelements Q5 and Q7) and a midpoint of the fourth arm (a connection pointof the adjustment switching elements Q6 and Q8). In the presentembodiment, the four adjustment switching elements Q5 to Q8 are each ann-channel depletion MOSFET.

More specifically, the source of the adjustment switching element Q5 andthe drain of the adjustment switching element Q6 are electricallyconnected to the first output point 213 of the inverter circuit 21 viathe first primary capacitor C11. The source of the adjustment switchingelement Q7 and the drain of the adjustment switching element Q8 areelectrically connected to the second output point 214 via the secondprimary capacitor C12 and the primary coil L1. The adjustment capacitorC1 has one end electrically connected to a connection point of the drainof the adjustment switching element Q5 and the drain of the adjustmentswitching element Q7. The adjustment capacitor C1 has the other endelectrically connected to a connection point of the source of theadjustment switching element Q6 and the source of the adjustmentswitching element Q8.

The four adjustment switching elements Q5 to Q8 are electricallyconnected to four diodes D5 to D8 respectively. The diode D5 iselectrically connected between the drain and the source of theadjustment switching element Q5. The diode D6 is electrically connectedbetween the drain and the source of the adjustment switching element Q6.The diode D7 is electrically connected between the drain and the sourceof the adjustment switching element Q7. The diode D8 is electricallyconnected between the drain and the source of the adjustment switchingelement Q8. The diodes D5 to D8 are connected to the adjustmentswitching elements Q5 to Q8 in such an orientation that the cathodes ofthe diodes D5 to D8 are adjacent to the drains of the adjustmentswitching elements Q5 to Q8, respectively. Here, the diodes D5 to D8 areparasitic diodes of the adjustment switching elements Q5 to Q8,respectively.

The control circuit 23 includes, for example, a microcomputer as a maincomponent. The microcomputer causes a Central Processing Unit (CPU) toexecute a program stored in a memory of the microcomputer to realize thefunction as the control circuit (controller) 23. The program may bestored in the memory of the microcomputer in advance, provided as arecording medium such as a memory card in which the program is stored,or provided via an electric communication line.

The control circuit 23 outputs the first drive signals G1 to G4 forswitching on/off respectively of the conversion switching elements Q1 toQ4 of the inverter circuit 21. The four first drive signals G1 to G4respectively correspond to the four conversion switching elements Q1 toQ4. Here, the control circuit 23 outputs the first drive signals G1 toG4 to the gates of the conversion switching elements Q1 to Q4 to controlthe conversion switching elements Q1 to Q4, respectively.

The control circuit 23 outputs the second drive signals G5 to G8 forswitching on/off respectively of the four adjustment switching elementsQ5 to Q8 of the variable capacitance circuit 22. The four second drivesignals G5 to G8 respectively correspond to the four adjustmentswitching elements Q5 to Q8. Here, the control circuit 23 outputs thesecond drive signals G5 to G8 to the gates of the adjustment switchingelements Q5 to Q8 to control the adjustment switching elements Q5 to Q8,respectively.

Note that in the present embodiment, the control circuit 23 directlyoutputs the first drive signals G1 to G4 and the second drive signals G5to G8 to the gates of the conversion switching elements Q1 to Q4 and theadjustment switching elements Q5 to Q8 respectively, but theconfiguration of the control circuit 23 is not limited to thisconfiguration. For example, the non-contact power supply apparatus 2 mayfurther include a drive circuit, and the drive circuit may receive thefirst drive signals G1 to G4 and the second drive signals G5 to G8 fromthe control circuit 23 to drive the conversion switching elements Q1 toQ4 and the adjustment switching elements Q5 to Q8 respectively.

The primary coil L1 is electrically connected in series to the pair ofprimary capacitors C11 and C12 and the variable capacitance circuit 22at the pair of output points 213 and 214 of the inverter circuit 21. Theprimary coil L1 has one end electrically connected to the first outputpoint 213 of the inverter circuit 21 via the variable capacitancecircuit 22 and the first primary capacitor C11. The primary coil L1 hasthe other end electrically connected to the second output point 214 ofthe inverter circuit 21 via the second primary capacitor C12.

The non-contact power supply apparatus 2 of the present embodimentfurther includes a meter 24 configured to measure the magnitude of acurrent flowing through the primary coil L1 as a measured value. Betweenthe primary coil L1 and the second primary capacitor C12, a currentsensor 25 including, for example, a current transformer is provided. Themeter 24 receives an output of the current sensor 25 and measures themagnitude of a current flowing through the primary coil L1 as themeasured value. The meter 24 is configured to output the measured valueto the control circuit 23. The control circuit 23 monitors the magnitudeof output power output from the primary coil L1 by using the measuredvalue measured by the meter 24.

<Basic Operation>

Next, with reference to FIGS. 1 and 2, basic operation of thenon-contact power supply apparatus 2 of the present embodiment will bedescribed. In FIG. 2, the horizontal axis is a time axis, and signalwaveforms of the first drive signals “G1, G4,” and “G2, G3” and thesecond drive signals “G5, G8,” and “G6, G7” are shown sequentially fromtop to bottom. Note that “ON” and “OFF” in FIG. 2 represent on and offof corresponding switching elements (the conversion switching elementsand the adjustment switching elements).

(1) Without Variable Capacitance Circuit

First, operation of the non-contact power supply apparatus 2 will bedescribed in the case where the variable capacitance circuit 22 is notprovided, that is, only the primary coil L1 and the pair of primarycapacitors C11 and C12 are electrically connected between the outputpoints 213 and 214 in the pair. The operation of the non-contact powersupply apparatus 2 in this case is equivalent to the operation of thenon-contact power supply apparatus 2 in the case where the operation ofthe variable capacitance circuit 22 is stopped in the circuitconfiguration of FIG. 1, that is, all the adjustment switching elementsQ5 to Q8 of the variable capacitance circuit 22 are fixed in an onstate.

As illustrated in FIG. 2, the control circuit 23 generates signals, asthe first drive signals G1 and G4 respectively corresponding to theconversion switching elements Q1 and Q4 and the first drive signals G2and G3 respectively corresponding to the conversion switching elementsQ2 and Q3, which are in anti-phase (with a phase difference of 180degrees) to each other. Thus, in the inverter circuit 21, a pair of thefirst conversion switching element Q1 and the fourth conversionswitching element Q4 and a pair of the second conversion switchingelement Q2 and the third conversion switching element Q3 are controlledto be alternately turned on.

As a result, a voltage (alternating-current voltage) whose polarity(positive/negative) is cyclically inverted is generated between theoutput points 213 and 214 in the pair in the inverter circuit 21. Insum, the inverter circuit 21 converts a direct-current voltage appliedto the pair of input points 211 and 212 into an alternating-currentvoltage by switching the plurality of conversion switching elements Q1to Q4 and outputs the alternating-current voltage from the pair ofoutput points 213 and 214. In the following description, as to theoutput voltage of the inverter circuit 21, a voltage at which the firstoutput point 213 of the pair of output points 213 and 214 has a highpotential is referred to as a “positive polarity.” and a voltage atwhich the second output point 214 has a high potential is referred to asa “negative polarity.” That is, the output voltage of the invertercircuit 21 is the positive polarity when the conversion switchingelements Q1 and Q4 are in the on state, whereas the output voltage ofthe inverter circuit 21 is the negative polarity when the conversionswitching elements Q2 and Q3 are in the on state.

As described above, the inverter circuit 21 outputs thealternating-current voltage from the pair of output points 213 and 214,so that an alternating current flows through the primary coil L1electrically connected between the output points 213 and 214 in thepair, and the primary coil L1 generates a magnetic field. This enablesthe non-contact power supply apparatus 2 to supply output power from theprimary coil L1 to the secondary coil L2 of the non-contact powerreception apparatus 3 in a non-contact manner.

However, when the variable capacitance circuit 22 is not provided, inthe non-contact power supply apparatus 2 of the present embodiment, theprimary coil L1 and the pair of primary capacitors C11 and C12 form aprimary resonance circuit. Thus, the magnitude of output power outputfrom the primary coil L1 changes depending on the operation frequency ofthe inverter circuit 21 (i.e., frequencies of the first drive signals G1to G4) and reaches a peak when the operation frequency of the invertercircuit 21 matches with the resonance frequency of the primary resonancecircuit.

Here, when a change in the relative positional relationship between theprimary coil L1 and the secondary coil L2 changes the couplingcoefficient between the primary coil L1 and the secondary coil L2, thefrequency characteristics of the output power of the non-contact powersupply apparatus 2 (hereinafter referred to as “resonancecharacteristics”) change. FIG. 3 shows a change in the resonancecharacteristics of the non-contact power supply apparatus 2 in the casewhere the relative positional relationship between the primary coil L1and the secondary coil L2 changes. Note that in FIG. 3, the horizontalaxis represents the frequency (the operation frequency of the invertercircuit 21), the vertical axis represents the output power of thenon-contact power supply apparatus 2, and the resonance characteristicsof the non-contact power supply apparatus 2 in the case of differentrelative positional relationship between the primary coil L1 and thesecondary coil L2 are denoted by “X1” and “X2.”

Here, as illustrated in FIG. 3, it is assumed that a frequency band(hereinafter referred to as an “allowed frequency band F1”) usable asthe operation frequency of the inverter circuit 21 is limited. Theallowed frequency band F1 is specified by, for example, a low such asthe radio act. In this case, frequencies lower than the lower limitvalue fmin of the allowed frequency band F1 and frequencies higher theupper limit value fmax of the allowed frequency band F1 is unusable asthe operation frequency of the inverter circuit 21. In such cases, whenthe resonance characteristics of the non-contact power supply apparatus2 are in, for example, a state as indicated by “X1” in FIG. 3, anyadjustment of the operation frequency of the inverter circuit 21 may notachieve a necessary magnitude (hereinafter referred to as a “targetvalue”) of the output power of the non-contact power supply apparatus 2.

For example, as illustrated in FIG. 4A, if the primary resonance circuithas a resonance frequency fr away from the allowed frequency band F1,the magnitude of the output power of the non-contact power supplyapparatus 2 does not reach the peak, and consequently, the output powermay be smaller than a target value P1. Alternatively, for example, asillustrated in FIG. 4B, even when the resonance frequency fr of theprimary resonance circuit is within the allowed frequency band F1, thepeak of the output power of the non-contact power supply apparatus 2does not reach the target value P1, and consequently, the output powermay be smaller than the target value P1. That is, in the examples ofFIGS. 4A and 4B, electric power in hatched (shaded) area is smaller thanthe target value P1.

Thus, the non-contact power supply apparatus 2 of the present embodimentis provided with the variable capacitance circuit 22 to render theresonance characteristics of the non-contact power supply apparatus 2variable and has a function of correcting the magnitude of the outputpower so as to satisfy the target value P1.

(2) With Variable Capacitance Circuit

Next, a description is given of operation of the non-contact powersupply apparatus 2 in the case where the variable capacitance circuit 22is provided as illustrated in FIG. 1, that is, the primary coil L1, thepair of primary capacitors C11 and C12, and the variable capacitancecircuit 22 are electrically connected between the output points 213 and214 in the pair.

As illustrated in FIG. 2, the control circuit 23 generates signals, asthe second drive signals G6 and G7 respectively corresponding to theadjustment switching elements Q6 and Q7 and the second drive signals G5and G8 respectively corresponding to the adjustment switching elementsQ5 and Q8, which are in anti-phase (with a phase difference of 180degrees) to each other. Thus, in the variable capacitance circuit 22, apair of the second adjustment switching element Q6 and the thirdadjustment switching element Q7 and a pair of the first adjustmentswitching element Q5 and the fourth adjustment switching element Q8 arecontrolled to be alternately turned on. In the present embodiment, thecontrol circuit 23 controls the frequencies of the first drive signalsG1 to G4 and the frequencies of the second drive signals G5 to G8 to beequal to each other.

When the output voltage of the inverter circuit 21 is the positivepolarity during a period during which the adjustment switching elementsQ5 and Q8 are on and the adjustment switching elements Q6 and Q7 areoff, a voltage is applied to the adjustment capacitor C1 via theadjustment switching elements Q5 and Q8. That is, a state (hereinafteralso referred to as a “first state”) is achieved where the primary coilL1 is electrically connected via the adjustment capacitor C1 between theoutput points 213 and 214 in the pair in the inverter circuit 21.

On the other hand, when the output voltage of the inverter circuit 21 isthe negative polarity during a period during which the adjustmentswitching elements Q5 and Q8 are on and the adjustment switchingelements Q6 and Q7 are off, a current flows through the diode D7 and theadjustment switching element Q5. That is, a state (hereinafter alsoreferred a “second state”) is achieved where the primary coil L1 iselectrically connected without the adjustment capacitor C1 between theoutput points 213 and 214 in the pair in the inverter circuit 21. Inother words, the both ends of the adjustment capacitor C1 are bypassedby the diode D7 and the adjustment switching element Q5.

Moreover, when the output voltage of the inverter circuit 21 is thepositive polarity during a period during which the adjustment switchingelements Q6 and Q7 are on and the adjustment switching elements Q5 andQ8 are off, a current flows through the adjustment switching element Q6and the diode D8. That is, a state (hereinafter also referred to as a“third state”) is achieved where the primary coil L1 is electricallyconnected without the adjustment capacitor C1 between the output points213 and 214 in the pair in the inverter circuit 21. In other words, theboth ends of the adjustment capacitor C1 are bypassed by the adjustmentswitching element Q6 and the diode D8.

On the other hand, when the output voltage of the inverter circuit 21 isthe negative polarity during a period during which the adjustmentswitching elements Q6 and Q7 are on and the adjustment switchingelements Q5 and Q8 are off, a voltage is applied to the adjustmentcapacitor C1 via the adjustment switching elements Q6 and Q7. That is, astate (hereinafter also referred to as a “fourth state”) is achievedwhere the primary coil L1 is electrically connected via the adjustmentcapacitor C1 between the output points 213 and 214 in the pair in theinverter circuit 21. Note that the polarity of the voltage applied tothe adjustment capacitor C1 is reversed between the first state and thefourth state.

As described above, the variable capacitance circuit 22 switches betweenthe state where the primary coil L1 is electrically connected via theadjustment capacitor C1 between the output points 213 and 214 in thepair and the state where the primary coil L1 is electrically connectedwithout the adjustment capacitor C1 between the output points 213 and214 in the pair. Thus, the magnitude of the capacity component betweenthe pair of output points 213 and 214 and the primary coil L1 apparentlychanges. Here, the state of the variable capacitance circuit 22 dependson on/off of the plurality of adjustment switching elements Q5 to Q8 andthe polarity of the output voltage of the inverter circuit 21. In sum,the variable capacitance circuit 22 adjusts the magnitude of thecapacity component between the pair of output points 213 and 214 and theprimary coil L1 by switching the plurality of adjustment switchingelements Q5 to Q8.

Thus, in the non-contact power supply apparatus 2 of the presentembodiment, the magnitude of the capacity component between the pair ofoutput points 213 and 214 and the primary coil L1 is adjusted by thevariable capacitance circuit 22 to enable a change in the resonancecharacteristics of the non-contact power supply apparatus 2. As aresult, when the output power of the non-contact power supply apparatus2 is smaller than the target value P1 as described above, the magnitudeof the output power can be corrected by the variable capacitance circuit22 so as to satisfy the target value P1.

Here, in the present embodiment, as described above, the first drivesignals G1 and G4 respectively corresponding to the conversion switchingelements Q1 and Q4 and the first drive signals G2 and G3 respectivelycorresponding to the conversion switching elements Q2 and Q3 are signalsin anti-phase (with a phase difference of 180 degrees) to each other.Similarly, the second drive signals G6 and G7 respectively correspondingto the adjustment switching elements Q6 and Q7 and the second drivesignals G5 and G8 respectively corresponding to the adjustment switchingelements Q5 and Q8 are signals in anti-phase (with a phase difference of180 degrees) to each other.

Here, a phase difference θ between the first drive signal and the seconddrive signal in the present embodiment is a delay of the phase of eachof the second drive signals G6 and G7 to the phase of each of the firstdrive signals G1 and G4 or a delay of the phase of each of the seconddrive signals G5 and G8 to the phase of each of the first drive signalsG2 and G3 (see FIG. 2). That is, since the delay of the phase of each ofthe second drive signals G6 and G7 to the phase of each of the firstdrive signals G1 and G4 and the delay of the phase of each of the seconddrive signals G5 and G8 to the phase of each of the first drive signalsG1 and G4 are different from each other by 180 degrees, the value of thephase difference θ varies depending on the delay of a phase defined asthe phase difference θ. Thus, in the present embodiment, the delay ofthe phase of each of the second drive signals G6 and G7 to the phase ofeach of the first drive signals G1 and G4 or the delay of the phase ofeach of the second drive signals G5 and G8 to the phase of each of thefirst drive signals G2 and G3 is defined as the phase difference θ.

Here, when all the first drive signals G1 and G4 and the second drivesignals G6 and G7 are “ON,” the third state is achieved where theprimary coil L1 is electrically connected without the adjustmentcapacitor C1 between the output points 213 and 214 in the pair in thevariable capacitance circuit 22. Alternatively, when all the first drivesignals G2 and G3 and the second drive signals G5 and G8 are “ON,” thesecond state is achieved where the primary coil L1 is electricallyconnected without the adjustment capacitor C1 between the output points213 and 214 in the pair in the variable capacitance circuit 22. That is,in the present embodiment, a phase difference for a combination of thefirst drive signals and the second drive signals which produces a statewhere the primary coil L1 is electrically connected without theadjustment capacitor C1 between the output points 213 and 214 in thepair is defined as the phase difference θ.

<Leading Phase Mode and Lagging Phase Mode>

Next, a leading phase mode and a lagging phase mode will be described.

(1) Without Variable Capacitance Circuit

First, similarly to item “Basic Operation,” the case where the variablecapacitance circuit 22 is not provided, that is, only the primary coilL1 and the pair of primary capacitors C11 and C12 are electricallyconnected between the output points 213 and 214 in the pair will bedescribed.

In this case, the inverter circuit 21 operates in an operation modewhich is either the lagging phase mode or the leading phase modedepending on, for example, the relationship between the operationfrequency of the inverter circuit 21 and the resonance frequency of theprimary resonance circuit.

The leading phase mode is a mode in which the inverter circuit 21operates with the phase of the output current (current flowing throughthe primary coil L1) of the inverter circuit 21 leading the phase of theoutput voltage of the inverter circuit 21. In the leading phase mode,the switching operation of the inverter circuit 21 is hard switching.Thus, in the leading phase mode, the switching loss of the conversionswitching elements Q1 to Q4 is likely to increase and stress is likelyto be applied to the conversion switching elements Q1 to Q4.

On the other hand, the lagging phase mode is a mode in which theinverter circuit 21 operates with the phase of the output current(current flowing through the primary coil L1) of the inverter circuit 21lagging the phase of the output voltage of the inverter circuit 21. Inthe lagging phase mode, the switching operation of the inverter circuit21 is soft switching. Thus, in the lagging phase mode, the switchingloss of the conversion switching elements Q1 to Q4 can be reduced, andstress is less likely to be applied to the conversion switching elementsQ1 to Q4. Thus, the operation of the inverter circuit 21 in the laggingphase mode is preferable to the operation of the inverter circuit 21 inthe leading phase mode.

(2) With Variable Capacitance Circuit

Next, the case where the variable capacitance circuit 22 is provided,that is, the primary coil L1, the pair of primary capacitors C11 andC12, and the variable capacitance circuit 22 are electrically connectedbetween the output points 213 and 214 in the pair will be described.

In this case, similarly to the inverter circuit 21, the variablecapacitance circuit 22 also operates in an operation mode which iseither the leading phase mode or the lagging phase mode. Also in thevariable capacitance circuit 22, operation in the lagging phase mode butnot in the leading phase mode is preferable.

It is confirmed that when the variable capacitance circuit 22 isprovided, the operation mode (lagging phase mode or leading phase mode)of each of the inverter circuit 21 and the variable capacitance circuit22 changes depending on the phase difference θ between each of the firstdrive signals G1 to G4 and each of the second drive signals G5 to G8.Moreover, the relationship between the operation mode of the invertercircuit 21 and the phase difference θ changes depending on the operationmode of the inverter circuit 21 in a state where the variablecapacitance circuit 22 is not provided, that is, under the conditiondescribed in “(1) Without Variable Capacitance Circuit.” In other words,the relationship between the operation frequency of the inverter circuit21 and the resonance frequency of the primary resonance circuitdetermines the operation mode of the inverter circuit 21, and therelationship between the operation mode of the inverter circuit 21 andthe phase difference θ changes depending on whether the operation modeof the inverter circuit 21 is the lagging phase mode or the leadingphase mode.

FIGS. 5A and 5B show the characteristics (phase differencecharacteristics) of the output power of the non-contact power supplyapparatus 2 with respect to the phase difference θ respectively in thecase where the inverter circuit 21 is in the leading phase mode withoutthe variable capacitance circuit 22 and in the case where the invertercircuit 21 is in the lagging phase mode without the variable capacitancecircuit 22. In FIGS. 5A and 5B, the horizontal axis represents the phasedifference θ between each of the first drive signals G1 to G4 and eachof the second drive signals G5 to G8, and the vertical axis representsthe output power of the non-contact power supply apparatus 2.

That is, when the inverter circuit 21 is in the leading phase modewithout the variable capacitance circuit 22 (hereinafter referred to asan “initial leading phase”), the output power of the non-contact powersupply apparatus 2 changes, for example, depending on the phasedifference θ as shown in FIG. 5A. In the example shown in FIG. 5A, theoutput power of the non-contact power supply apparatus 2 changesdepending on the phase difference so as to be local maximum and maximumwhen the phase difference θ is 90 degrees and so as to be local minimumand minimum when the phase difference θ is 180 degrees. The principle ofchanging of the output power of the non-contact power supply apparatus 2depending on the phase difference θ will be described in item “(2)Principle of Output Power Control by Phase Difference Control” below.Here, the phase difference θ (0 degrees to 360 degrees) is divided intofour zones, that is, a first zone Z1 extending from 0 degrees to 90degrees, a second zone Z2 extending from 90 degrees to 180 degrees, athird zone Z3 extending from 180 degrees to 270 degrees, and a fourthzone Z4 extending from 270 degrees to 360 degrees. In this case, therelationship between the operation mode (lagging phase mode or leadingphase mode) of the inverter circuit 21 and each zone of the phasedifference θ is shown in Table 1.

TABLE 1 Z1 (0-90) Z2 (90-80) Z3 (180-270) Z4 (270-360) Inverter LeadingLagging Leading Leading Circuit Phase Phase Phase Phase Mode Mode ModeMode

In sum, in the case of “initial leading phase,” the inverter circuit 21operates in the lagging phase mode only in the second zone Z2 in whichthe phase difference θ is 90 degrees to 180 degrees of the first zone Z1to fourth zone Z4.

On the other hand, when the inverter circuit 21 is in the lagging phasemode without the variable capacitance circuit 22 (hereinafter referredto as an “initial lagging phase”), the output power of the non-contactpower supply apparatus 2 changes depending on, for example, the phasedifference θ as illustrated in FIG. 5B. In the example shown in FIG. 5B,the output power of the non-contact power supply apparatus 2 changesdepending on the phase difference θ so as to be local maximum andmaximum when the phase difference θ is 270 degrees and so as to be localminimum and minimum when the phase difference θ is 180 degrees. In thiscase, the relationship between the operation mode (lagging phase mode orleading phase mode) of each of the inverter circuit 21 and the variablecapacitance circuit 22 and each zone of the phase difference θ is shownin Table 2.

TABLE 2 Z1 (0-90) Z2 (90-80) Z3 (180-270) Z4 (270-360) Inverter LaggingLagging Leading Lagging Circuit Phase Phase Phase Phase Mode Mode ModeMode Variable Lagging Leading Lagging Lagging Capacitance Phase PhasePhase Phase Circuit Mode Mode Mode Mode

In sum, in the case of the “initial lagging phase,” the inverter circuit21 operates in the lagging phase mode in three zones, the first zone Z1and the second zone Z2 in which the phase difference θ is 0 degrees to180 degrees and the fourth zone Z4 in which the phase difference θ is270 degrees to 360 degrees of the first zone Z1 to the fourth zone Z4.Moreover, in the case of the “initial lagging phase,” the variablecapacitance circuit 22 operates in the lagging phase mode in threezones, the first zone Z1 in which the phase difference θ is 0 degrees to90 degrees and the third zone Z3 and the fourth zone Z4 in which thephase difference θ is 180 degrees to 360 degrees of the first zone Z1 tothe fourth zone Z4. That is, in the case of the “initial lagging phase,”both the inverter circuit 21 and the variable capacitance circuit 22operate in the lagging phase mode in two zones, the first zone Z1 inwhich the phase difference θ is 0 degrees to 90 degrees and the fourthzone Z4 in which the phase difference θ is 270 degrees to 360 degrees ofthe first zone Z1 to the fourth zone Z4.

<Output Power Control>

Next, operation of “output power control” of adjusting the magnitude ofan output power in the non-contact power supply apparatus 2 of thepresent embodiment will be described.

(1) Frequency Control and Phase Difference Control

In the present embodiment, the control circuit 23 is configured toadjust the magnitude of the output power by two methods, “frequencycontrol” for controlling the frequencies of the first drive signals G1to G4 and the second drive signals G5 to G8 and “phase differencecontrol” for adjusting the phase difference θ.

In the present embodiment, the control circuit 23 first adjusts thefrequencies of the first drive signals G1 to G4 and the second drivesignals G5 to G8 to perform the frequency control of adjusting themagnitude of the output power. That is, as described in item “(1)Without Variable Capacitance Circuit” in “Basic Operation,” themagnitude of the output power output from the primary coil L1 changesdepending on the operation frequency of the inverter circuit 21 (i.e.,the frequencies of the first drive signals G1 to G4) (see FIG. 3). Thus,in the frequency control, the control circuit 23 adjusts the frequenciesof the first drive signals G1 to G4 and the second drive signals G5 toG8 to adjust the operation frequency of the inverter circuit 21 and toadjust the magnitude of the output voltage.

Here, when the frequency band (allowed frequency band F1) usable as theoperation frequency of the inverter circuit 21 is limited, frequenciesadjustable by the frequency control are limited within the allowedfrequency band F1. When the magnitude of the output power afteradjustment by the frequency control is smaller than the prescribedtarget value, the control circuit 23 performs the phase differencecontrol described below. That is, when only the frequency controlresults in the output power smaller than the target value (see FIGS. 4Aand 4B), the control circuit 23 compensates for the shortfall by thephase difference control.

In the phase difference control, the control circuit 23 adjusts thephase difference θ, which is a delay of the phase of each of the seconddrive signals G6 and G7 (G5, G8) to the phase of each of the first drivesignals G1 and G4 (G2, G3), to a set value within a prescribed range soas to adjust the magnitude of the output power of the non-contact powersupply apparatus 2. Here, the prescribed range includes at least one ofa range of 270 degrees to 360 degrees and a range of 90 degrees to 180degrees.

That is, as can be clearly seen from FIGS. 5A and 5B, the output powerof the non-contact power supply apparatus 2 changes depending on thephase difference θ, and therefore, adjusting the phase difference θ tothe set value by the control circuit 23 enables adjustment of themagnitude of the output power. Note that the phase difference θ betweeneach of the first drive signals G1 to G4 and each of the second drivesignals G5 to G8, as described above, also affects the operation mode(lagging phase mode or leading phase mode) of each of the invertercircuit 21 and the variable capacitance circuit 22. Thus, to operate theinverter circuit 21 and the variable capacitance circuit 22 in thelagging phase mode, the range of the phase difference θ has to belimited.

First, with reference to FIG. 5A, the case of “initial leading phase”will be described. In this case, as described above, the invertercircuit 21 operates in the lagging phase mode only in the second zone Z2in which the phase difference θ is 90 degrees to 180 degrees of thefirst zone Z1 to the fourth zone Z4. Thus, in the case of the “initialleading phase,” the prescribed range is preferably a range of 90 degreesto 180 degrees. Thus, the inverter circuit 21 can operate in the laggingphase mode when the control circuit 23 adjusts the phase difference θ tothe set value within the prescribed range to adjust the magnitude of theoutput power of the non-contact power supply apparatus 2.

Next, with reference to FIG. 5B, the case of “initial lagging phase”will be described. In this case, as described above, the invertercircuit 21 operates in the lagging phase mode in three zones, the firstzone Z1, the second zone Z2, and the fourth zone Z4. Note that in thefirst zone Z1 in which the phase difference θ is 0 degrees to 90degrees, the magnitude of the output power only slightly changes evenwhen the phase difference θ changes. Thus, in order to adjust themagnitude of the output power by adjusting the phase difference θ, thephase difference θ has to be adjusted in two zones, the second zone Z2in which the phase difference θ is 90 degrees to 180 degrees and thefourth zone Z4 in which the phase difference θ is 270 degrees to 360degrees. Thus, when the prescribed range is a range of 270 degrees to360 degrees and a range of 90 degrees to 180 degrees, the invertercircuit 21 is operable in the lagging phase mode when the controlcircuit 23 adjusts the phase difference θ to the set value within theprescribed range to adjust the magnitude of the output power of thenon-contact power supply apparatus 2.

Moreover, in the case of the “initial lagging phase,” as describedabove, both the inverter circuit 21 and the variable capacitance circuit22 operate in the lagging phase mode in two zones, the first zone Z1 inwhich the phase difference θ is 0 degrees to 90 degrees and in thefourth zone Z4 in which the phase difference θ is 270 degrees to 360degrees. As described above, in the first zone Z11, the magnitude of theoutput power does not substantially change although the phase differenceθ changes. Thus, adjusting the phase difference θ enables adjustment ofthe magnitude of the output power only in the fourth zone Z4 of the twozones, the first zone Z1 and the fourth zone Z4. Thus, in the case ofthe “initial lagging phase,” the prescribed range is preferably therange of 270 degrees to 360 degrees. Thus, both the inverter circuit 21and the variable capacitance circuit 22 can operate in the lagging phasemode when the control circuit 23 adjusts the phase difference θ to theset value within the prescribed range to adjust the magnitude of theoutput power of the non-contact power supply apparatus 2.

In sum, in the case of the “initial leading phase,” the prescribed rangeis preferably a range of 90 degrees to 180 degrees (second zone Z2). Onthe other hand, in the case of the “initial lagging phase,” theprescribed range is preferably a range of 90 degrees to 180 degrees(second zone Z2) or a range of 270 degrees to 360 degrees (fourth zoneZ4). In the case of the “initial lagging phase,” the prescribed range ismore preferably the range of 270 degrees to 360 degrees (fourth zoneZ4).

Moreover, in a zone (at least one of the second zone Z2 and the fourthzone Z4) in which the inverter circuit 21 operates in the lagging phasemode, as illustrated in FIGS. 5A and 5B, the output power increases asthe phase difference θ is reduced. Thus, for example, when theprescribed range is the second zone Z2 (90 degrees to 180 degrees), thecontrol circuit 23 preferably gradually lowers the set value within theprescribed range such that the phase difference θ is gradually reducedfrom the upper limit value (180 degrees) to the lower limit value (90degrees) within the prescribed range. Similarly, when the prescribedrange is the fourth zone Z4 (270 degrees to 360 degrees), the controlcircuit 23 preferably gradually lowers the set value within theprescribed range such that the phase difference θ is gradually reducedfrom the upper limit value (360 degrees) to the lower limit value (270degrees) within the prescribed range. Thus, as the control circuit 23gradually changes (lowers) the set value within the prescribed range,the output power of the non-contact power supply apparatus 2 graduallyincreases.

(2) Principle of Output Power Control by Phase Difference Control

With reference to FIGS. 6A to 8, the principle that the control circuit23 adjusts the phase difference θ to a set value within a prescribedrange by phase difference control to control the magnitude of the outputpower of the non-contact power supply apparatus 2 will be describedbelow.

The output power of the non-contact power supply apparatus 2 changesdepending on a voltage applied to the primary coil L1 of the primaryresonance circuit. The voltage applied to the primary coil L1 is acomposite voltage of the output voltage of the inverter circuit 21 andthe voltage across the variable capacitance circuit 22 (voltage betweenthe drain of the adjustment switching element Q5 and the drain of theadjustment switching element Q7). Thus, when the output voltage of theinverter circuit 21 and the voltage across the variable capacitancecircuit 22 have the same polarity and enhance each other, the voltageapplied to the primary coil L1 increases, so that the output power ofthe non-contact power supply apparatus 2 increases. In this case, as thevoltage across the adjustment capacitor C1 increases, the voltage acrossthe variable capacitance circuit 22 and the voltage applied to theprimary coil L1 increase, and therefore, the output power of thenon-contact power supply apparatus 2 increases. Thus, in the phasedifference control, the control circuit 23 adjusts the phase differenceθ to change the balance of charging and discharging of the adjustmentcapacitor C1 and to change the voltage across the adjustment capacitorC1, thereby changing the output power of the non-contact power supplyapparatus 2.

Here, whether the adjustment capacitor C1 is charged or discharged isdetermined depending on on/off of the plurality of adjustment switchingelements Q5 to Q8 and the orientation of the output current of theinverter circuit 21. The output current of the inverter circuit 21 is acurrent flowing through the primary coil L1 and is thus hereinafter alsoreferred to as a “primary current I1.” The orientation of the primarycurrent I1 flowing from the first output point 213 through the primarycapacitor C11, the variable capacitance circuit 22, the primary coil L1,and the primary capacitor C12 to the second output point 214, that is,the orientation of the primary current I1 indicated by the arrow in FIG.1 is referred to as a “positive direction.” The orientation of theprimary current I1 flowing from the second output point 214 through theprimary capacitor C12, the primary coil L1, the variable capacitancecircuit 22, and the primary capacitor C11 to the first output point 213,that is, the orientation opposite to the orientation of the primarycurrent I1 indicated by the arrow in FIG. 1 is referred to as a“negative direction.”

FIGS. 6A to 6D show combination patterns of on/off of the plurality ofadjustment switching elements Q5 to Q8 and directions of the primarycurrent I1. In FIGS. 6A to 6D, solid arrows represent current paths, andthe adjustment switching elements circled by a dotted line representelements in an on state.

FIG. 6A shows the variable capacitance circuit 22 in which theadjustment switching elements Q6 and Q7 are on, the adjustment switchingelements Q5 and Q8 are off, and the primary current I1 in the negativedirection flows (hereinafter referred to as a “first charge mode”). FIG.6B shows the variable capacitance circuit 22 in which the adjustmentswitching elements Q6 and Q7 are on, the adjustment switching elementsQ5 and Q8 are off, and the primary current I1 in the positive directionflows (hereinafter referred to as a “first discharge mode”). FIG. 6Cshows the variable capacitance circuit 22 in which the adjustmentswitching elements Q5 and Q8 are on, the adjustment switching elementsQ6 and Q7 are off, and the primary current I1 in the positive directionflows (hereinafter referred to as a “second charge mode”). FIG. 6D showsthe variable capacitance circuit 22 in which the adjustment switchingelements Q5 and Q8 are on, the adjustment switching elements Q6 and Q7are off, and the primary current I1 in the negative direction flows(hereinafter referred to as a “second discharge mode”). In the firstcharge mode shown in FIG. 6A and the second charge mode shown in theFIG. 6C, the adjustment capacitor C1 is charged. On the other hand, inthe first discharge mode shown in FIG. 6B and the second discharge modeshown in FIG. 6D, the adjustment capacitor C1 is discharged.

Next, with reference to FIGS. 7 and 8, the relationship between thephase difference θ and the balance of charging and discharging of theadjustment capacitor C1 will be described. Both in FIG. 7 and FIG. 8,the horizontal axis is a time axis, and waveforms of the first drivesignals “G1, G4,” the primary current “I1,” and two types of the seconddrive signals “G6, G7” are shown sequentially from top to bottom. Thetwo types of the second drive signals here are different in the phasedifferences θ. Note that “ON” and “OFF” in FIGS. 7 and 8 represent onand off of the corresponding switching elements (conversion switchingelements and adjustment switching elements).

FIG. 7 shows an example in the case of the “initial lagging phase” and adelay (hereinafter referred to as a “voltage-current phase difference”)Φ of the phase of the primary current I1 to the phase of the outputvoltage of the inverter circuit 21 being 90 degrees. In FIG. 7, as thewaveforms of the two types of the second drive signals “G6, G7,” awaveform when the phase difference θ is 360 degrees and a waveform whenthe phase difference θ is 320 degrees are shown sequentially from top tobottom. Moreover, in FIG. 7, in the case of the phase difference θ being360 degrees, a period of the first charge mode is denoted by “Tca1,” aperiod of the first discharge mode is denoted by “Tda1,” a period of thesecond charge mode is denoted by “Tca2,” and a period of the seconddischarge mode is denoted by “Tda2.” Similarly, in the case of the phasedifference θ being 320 degrees, a period of the first charge mode isdenoted by “Tcb1,” a period of the first discharge mode is denoted by“Tdb1,” a period of the second charge mode is denoted by “Tcb2,” and aperiod of the second discharge mode is denoted by “Tdb2.”

As can be clearly seen from FIG. 7, when the phase difference θ is 360degrees, substantial equilibrium is achieved between a time period forcharging the adjustment capacitor C1 (hereinafter referred to as a“charging time period”) and a time period for discharging the adjustmentcapacitor C1 (hereinafter referred to as a “discharging time period”) inone cycle of the second drive signal. That is, when the phase differenceθ is 360 degrees, the total of “Tca1” and “Tca2” is substantially thesame length as the total of “Tda1” and “Tda2.” On the other hand, whenthe phase difference θ is 320 degrees, in one cycle of the second drivesignal, the charging time period exceeds the discharging time period.That is, when the phase difference θ is 320 degrees, the total of “Tcb1”and “Tcb2” is longer than the total of “Tdb1” and “Tdb2.”

Thus, when the phase difference θ changes from the 360 degrees toapproach 270 degrees, in one cycle of the second drive signal, theequilibrium between the charging time period and the discharging timeperiod is disturbed, and the proportion of the charging time periodgradually increases. As the charging time period increases with respectto the discharging time period, the voltage across the adjustmentcapacitor C1 increases. Thus, as a result, as the phase difference θapproaches from 360 degrees to 270 degrees, the output power of thenon-contact power supply apparatus 2 gradually increases.

Moreover, FIG. 8 shows an example in the case of the “initial laggingphase” and the voltage-current phase difference Φ being 45 degrees. InFIG. 8, as the waveforms of the two types of the second drive signals“G6, G7,” a waveform when the phase difference θ is 315 degrees and awaveform when the phase difference θ is 290 degrees are shownsequentially from top to bottom. Moreover, in FIG. 8, in the case of thephase difference θ being 315 degrees, a period of the first charge modeis denoted by “Tca1,” a period of the first discharge mode is denoted by“Tda1,” a period of the second charge mode is denoted by “Tca2,” and aperiod of the second discharge mode is denoted by “Tda2.” Similarly, inthe case of the phase difference θ being 290 degrees, a period of thefirst charge mode is denoted by “Tcb1,” a period of the first dischargemode is denoted by “Tdb1,” a period of the second charge mode is denotedby “Tcb2,” and a period of the second discharge mode is denoted by“Tdb2.”

When the voltage-current phase difference Φ is 45 degrees, as can beclearly seen from FIG. 8, substantial equilibrium is achieved betweenthe charging time period and the discharging time period in one cycle ofthe second drive signal even when the phase difference θ is 315 degrees.That is, even when the phase difference θ is 315 degrees, the total of“Tca1” and “Tca2” is substantially the same length as the total of“Tda1” and “Tda2.” On the other hand, when the phase difference θ is 290degrees, in one cycle of the second drive signal, the charging timeperiod exceeds the discharging time period. That is, when the phasedifference θ is 290 degrees, the total of “Tcb1” and “Tcb2” is longerthan the total of “Tdb1” and “Tdb2.”

Thus, not only in the case of the voltage-current phase difference Φbeing 90 degrees but also in the case of the “initial lagging phase,”when the phase difference θ changes from 360 degrees to approach 270degrees, in one cycle of the second drive signal, the equilibriumbetween the charging time period and the discharging time period isdisturbed, and the proportion of the charging time period graduallyincreases. Note that in the case of the voltage-current phase differenceΦ being 90 degrees, the charging time period exceeds the dischargingtime period with the phase difference θ being 320 degrees, whereas inthe case of the voltage-current phase difference Φ being 45 degrees, theequilibrium between the charging time period and the discharging timeperiod is achieved even with the phase difference θ being 315 degrees.As described above, when the phase difference θ is gradually reducedfrom 360 degrees, a phase difference θ (hereinafter referred to as a“change start point”) corresponding to an inflection point variesdepending on the voltage-current phase difference Φ. The inflectionpoint is a point at which the equilibrium between the charging timeperiod and the discharging time period is disturbed, and the voltageacross the adjustment capacitor C1 starts increasing. The change startpoint shifts toward 270 degrees when the voltage-current phasedifference Φ is 45 degrees more than when the voltage-current phasedifference Φ is 90 degrees, that is, the smaller the voltage-currentphase difference Φ is, the more the change start point shifts toward 270degrees.

That is, in the case of the “initial lagging phase,” the change startpoint is located within the prescribed range (e.g., 270 degrees to 360degrees), notwithstanding variations depending on the voltage-currentphase difference Φ. Thus, when the control circuit 23 gradually reducesthe phase difference θ from the upper limit value (360 degrees) of theprescribed range toward the lower limit value (270 degrees) of theprescribed range, the output power of the non-contact power supplyapparatus 2 gradually increases after the phase difference θ reaches thechange start point.

Moreover, in FIGS. 7 and 8, the case of the “initial lagging phase” hasbeen described, but the case of the “initial leading phase” isequivalent to the case where the phase of the primary current I1 isshifted by 180 degrees with reference to the example of the “initiallagging phase.” That is, shifting the phase of the primary current I1 by180 degrees in the example shown in FIGS. 7 and 8 results in an exampleof the “initial leading phase.” Thus, also in the case of the “initialleading phase,” the change start point is located within the prescribedrange (180 degrees to 90 degrees), notwithstanding variations dependingon the voltage-current phase difference Φ. Thus, when the controlcircuit 23 gradually reduces the phase difference θ from the upper limitvalue (180 degrees) of the prescribed range toward the lower limit value(90 degrees) of the prescribed range, the output power of thenon-contact power supply apparatus 2 gradually increases after the phasedifference θ reaches the change start point.

According to the above-described principle, in both of the cases of the“initial lagging phase” and the “initial leading phase,” the controlcircuit 23 adjusts the phase difference θ to the set value within theprescribed range by the phase difference control to adjust the magnitudeof the output power of the non-contact power supply apparatus 2.

(3) Overall Flow of Output Power Control

With reference to the flowchart shown in FIG. 9 illustrating processesin the control circuit 23, an overall flow of the “output power control”of the present embodiment will be described below.

When the output power control is started, the control circuit 23 firstcompares the prescribed target value with the magnitude of the outputpower (S1). If the output power is within an allowable error range(±several percents) of the target value (S1: rated power), the outputpower control is terminated.

If the output power is lower than the lower limit of the allowable errorrange of the target value (S1: shortfall), the control circuit 23 firstadjusts the output power by frequency control. Specifically the controlcircuit 23 compares the operation frequency f1 (i.e., the frequencies ofthe first drive signals G1 to G4) of an inverter with the lower limitvalue fmin of the allowed frequency band F1 (S11). If the operationfrequency f1 is higher than the lower limit value fmin (S11: Yes), thecontrol circuit 23 lowers the operation frequency f1 of the inverter bythe prescribed value Δf (S12) and returns to the operation in processS1. The control circuit 23 repeats these processes (S11 and S12) togradually lower the operation frequency f1, thereby enabling a gradualincrease in the output power, that is, approximation of the output powerto the target value. Note that the initial value of the operationfrequency f1 is, for example, the upper limit value fmax of the allowedfrequency band F1.

When the operation frequency f1 decreases to or lower than the lowerlimit value fmin in the frequency control (S11: No), the control circuit23 next adjusts the output power by phase difference control.Specifically, the control circuit 23 compares the phase difference θwith the lower limit value of the prescribed range (S13). Here, if theprescribed range is a range of 270 degrees to 360 degrees, the initialvalue of the phase difference θ is 360 (degrees), and the lower limitvalue of the prescribed range is 270 (degrees). If the prescribed rangeis a range of 90 degrees to 180 degrees, the initial value of the phasedifference θ is 180 (degrees), and the lower limit value of theprescribed range is 90 (degrees). If the phase difference θ is greaterthan or equal to the lower limit value (S13: No), the control circuit 23decrements (θ−1) the phase difference θ (S14) and returns to theoperation in process S1. The control circuit 23 repeats these processes(S13 and S14) to gradually reduce the phase difference θ, therebyenabling a gradual increase in the output power, that is, approximationof the output power to the target value.

Note that if in the phase difference control, the phase difference θbecomes lower than the lower limit value (S13: Yes), the control circuit23 determines an error (S15) and terminates the output power control.

If the output power exceeds the upper limit of the allowable error rangeof the target value (S1: excess), the control circuit 23 first adjuststhe output power by the phase difference control. Specifically, thecontrol circuit 23 compares the phase difference θ with the upper limitvalue of the prescribed range (S21). Here, when the prescribed range isa range of 270 degrees to 360 degrees, the upper limit value of theprescribed range is 360 (degrees), and when the prescribed range is arange of 90 degrees to 180 degrees, the upper limit value of theprescribed range is 180 (degrees). If the phase difference θ is lessthan or equal to the upper limit value (S21: No), the control circuit 23increments (θ+1) the phase difference θ (S22) and returns to theoperation in process S. The control circuit 23 repeats these processes(S21 and S22) to gradually increase the phase difference θ, therebyenabling a gradual reduction in the output power, that is, approximationof the output power to the target value.

If the phase difference θ exceeds the upper limit value in the phasedifference control (S21: Yes), the control circuit 23 then adjusts theoutput power by the frequency control. Specifically, the control circuit23 compares the operation frequency f1 (i.e., frequencies of the firstdrive signals G1 to G4) of an inverter with the upper limit value fmaxof the allowed frequency band F1 (S23). If the operation frequency f1 islower than the upper limit value fmax (S23: Yes), the control circuit 23increases the operation frequency f1 of the inverter by the prescribedvalue Δf (S24) and returns to the operation in process S1. The controlcircuit 23 repeats these processes (S23 and S24) to gradually increasethe operation frequency f1, thereby enabling a gradual reduction in theoutput power, that is, approximation of the output power to the targetvalue.

Note that if the operation frequency f1 is greater than or equal to theupper limit value fmax in the frequency control (S23: No), the controlcircuit 23 determines an error (S25) and terminates the output powercontrol.

Moreover, for the non-contact power supply apparatus 2, it is notessential that when the control circuit 23 adjusts the output power bythe phase difference control, the upper limit value of the prescribedrange is defined as an initial value, and the phase difference θ isgradually reduced from the initial value (the upper limit value of theprescribed range). For example, in the case where the prescribed rangeis a range of 270 degrees to 360 degrees, a value (e.g., 370 degrees)exceeding the upper limit value of the prescribed range may be definedas an initial value, and the control circuit 23 may gradually reduce thephase difference θ from the initial value. Alternatively, in the casewhere the prescribed range is a range of 270 degrees to 360 degrees, avalue (e.g., 315 degrees) smaller than the upper limit value of theprescribed range may be defined as an initial value, and the controlcircuit 23 may gradually reduce the phase difference θ from the initialvalue. In both of the cases, in an area between the change start pointlocated within the prescribed range and the lower limit value of theprescribed range, the output power of the non-contact power supplyapparatus 2 changes depending on the change of the phase difference θ.

<Start-Up Process>

The non-contact power supply apparatus 2 of the present embodimentcauses soft-start of the inverter circuit 21 as described below atstart-up in which the inverter circuit 21 and the variable capacitancecircuit 22 start operating.

At the start-up of the inverter circuit 21, the control circuit 23gradually increases the duty ratio of the first drive signals G1 to G4for controlling the conversion switching elements Q1 to Q4 from 0 (zero)to a prescribed value (e.g., 0.5) to realize the soft-start of theinverter circuit 21. This reduces an abrupt change of a voltage and/or acurrent input to the non-contact power supply apparatus 2 to enable areduction in stress applied to the circuit element. In the followingdescription, a process of changing the duty ratio of the first drivesignals G1 to G4 by the control circuit 23 as described above to realizethe soft-start of the inverter circuit 21 is referred to as a “start-upprocess.”

While the control circuit 23 performs the start-up process, thenon-contact power supply apparatus 2 of the present embodiment fixes allthe adjustment switching elements Q5 to Q8 of the variable capacitancecircuit 22 to an on state to disable the functions of the variablecapacitance circuit 22. This brings the non-contact power supplyapparatus 2 into a state equivalent to the state described in “(1)Without Variable Capacitance Circuit” (see item “Basic Operation”).

When the start-up process ends, that is, when the duty ratio of thefirst drive signals G1 to G4 reach the prescribed value (e.g., 0.5), thecontrol circuit 23 also starts the operation of the variable capacitancecircuit 22. In sum, after the start-up process ends, the control circuit23 starts controlling the adjustment switching elements Q5 to Q8 by thesecond drive signals G5 to G8. This brings the non-contact power supplyapparatus 2 into a state equivalent to the state described in “(2) WithVariable Capacitance Circuit” (see item “Basic Operation”). Here, if theprescribed range is within a range of 270 degrees to 360 degrees, thecontrol circuit 23 sets the phase difference θ to 360 (degrees) which isan initial value, and the control circuit 23 causes the variablecapacitance circuit 22 to start operating.

Now, when the start-up process as described above is performed, thecontrol circuit 23 preferably adjusts the output power by the frequencycontrol after the start-up process ends and before the operation of thevariable capacitance circuit 22 is started. That is, the control circuit23 adjusts the output power by the frequency control after the start-upprocess ends and before the operation of the variable capacitancecircuit 22 is started, and when the magnitude of the output power afteradjustment by the frequency control is less than the prescribed targetvalue, the control circuit 23 preferably causes the variable capacitancecircuit 22 to start operating. In this case, after the operation of thevariable capacitance circuit 22 is started, the control circuit 23adjusts the output power by the phase difference control. With thisconfiguration, if the magnitude of the output power reaches the targetvalue only by the frequency control, the control circuit 23 does notcause the variable capacitance circuit 22 to operate. Thus, it ispossible to avoid a reduction in the efficiency (power conversionefficiency) due to the variable capacitance circuit 22.

<Search Mode>

In the present embodiment, the control circuit 23 further has a searchmode for estimating a coupling coefficient between the primary coil L1and the secondary coil L2 in addition to the normal mode (including thestart-up process) for performing the output power control as describedabove. In the search mode, the control circuit 23 is configured togradually change the phase difference θ within the prescribed range andto estimate the coupling coefficient on the basis of the change of themeasured value (measured value of meter 24) along with the change of thephase difference θ. The measured value here is the magnitude of acurrent (hereinafter also referred to as a “coil current”) flowingthrough the primary coil L1 and is measured by the meter 24. The searchmode will be described in detail below.

As illustrated in FIGS. 10A and 10B, it is confirmed that therelationship between the coil current and the phase difference θ betweeneach of the second drive signals G5 to G8 and each of the first drivesignals G1 to G4 changes depending on the coupling coefficient betweenthe primary coil L1 and the secondary coil L2. In FIGS. 10A and 10B, thehorizontal axis represents the phase difference θ between the firstdrive signals G1 to G4 and the second drive signals G5 to G8, and thevertical axis represents the coil current (current flowing through theprimary coil L1). In FIGS. 10A and 10B, “Y1” to “Y5” represent therelationship between the phase difference θ and the coil current incases where coupling coefficients are different from each other. FIG.10B is an enlarged view of the area A1 of FIG. 10A.

Here, when “Y1” to “Y5” in FIGS. 10A and 10B are arranged in the orderof a larger coupling coefficient, “Y1” to “Y5” are arranged in the orderof Y5, Y4, Y3, Y2, and Y1. As can be clearly seen from FIG. 10B, whenthe phase difference θ is gradually reduced from the upper limit value(here 360 degrees) of the prescribed range, a phase difference θcorresponding to the inflection point at which the coil current startsincreasing varies depending on the coupling coefficient. As the couplingcoefficient between the primary coil L1 and the secondary coil L2increases, the phase difference θ at which the coil current startsincreasing decreases. Thus, using the relationship between the phasedifference θ and the coil current as shown in FIGS. 10A and 10B enablesthe control circuit 23 to estimate the coupling coefficient from thechange in the measured value (the magnitude of the coil current) alongwith the change of the phase difference θ.

Specifically, storing the relationship between the phase difference θand the coil current as shown in FIGS. 10A and 10B as characteristicdata, for example, in a table format, in a memory of a microcomputerenables the control circuit 23 to estimate the coupling coefficient byusing the characteristic data. When the load is an electric vehicle,such characteristic data varies depending on types of the vehicle, andtherefore, pieces of characteristic data of a plurality of types ofvehicles are preferably stored. Note that the non-contact power supplyapparatus 2 may communicate with the non-contact power receptionapparatus 3 to obtain the characteristic data from the non-contact powerreception apparatus 3.

The control circuit 23 can further estimate, from the couplingcoefficient, the resonance characteristics (i.e., the relationshipbetween the operation frequency of the inverter circuit 21 and theoutput power of the non-contact power supply apparatus 2) as describedin item “(1) With Variable Capacitance Circuit” of “Basic Operation”. Asa result, the control circuit 23 can estimate a frequency range in whichthe inverter circuit 21 operates in the lagging phase mode (i.e., not inthe leading phase mode), for example, for the operation frequency f1 ofthe inverter circuit 21. Thus, the control circuit 23 preferablyoperates in the above-described search mode before starting operation inthe normal mode. In this way, the control circuit 23 can set the initialvalue of the operation frequency f1 in starting the operation in thenormal mode to be within the frequency range in which the invertercircuit 21 operates in the lagging phase mode. Note that in this case,the lower limit value of the operation frequency f1 in theabove-described frequency control is a larger one of the lower limitvalue of the frequency range in which the inverter circuit 21 operatesin the lagging phase mode and the lower limit value fmin of the allowedfrequency band F1.

With reference to the flowchart in FIG. 11 showing the process of thecontrol circuit 23, an overall flow of the “search mode” of the presentembodiment will be described below. Note that the process shown in FIG.11 is performed before process S1 in the flowchart of FIG. 9 and beforethe start-up process.

When the search mode is started, the control circuit 23 first sets thephase difference θ to an initial value (here, 360 degrees) (S31). Then,the control circuit 23 decrements (θ−1) the phase difference θ (S32) toobtain a measured value of the coil current from the meter 24 (S33).Next, the control circuit 23 obtains a difference between a mostrecently measured value of the coil current and a previously measuredvalue of the coil current as an increment of the coil current andcompares the increment of the coil current with a threshold (S34). Here,if the increment of the coil current is less than the threshold (S34:No), the operation of the control circuit 23 returns to process S32.

If the increment of the coil current is greater than the threshold (S34:Yes), the control circuit 23 compares a current phase difference θ witha characteristic table (characteristic data in a table format) (S35).This enables the control circuit 23 to estimate the coupling coefficientand also to estimate the resonance characteristics from the couplingcoefficient. Next, the control circuit 23 returns the phase difference θto the initial value (here, 360 degrees) (S36) and terminates the searchmode.

<Effects>

As described above, the non-contact power supply apparatus 2 of thepresent embodiment provides the advantage that even when the relativepositional relationship between the primary coil L1 and the secondarycoil L2 changes, required electric power is easily secured. That is, thenon-contact power supply apparatus 2 adjusts the phase difference θ,which is a delay of the phase of each of the second drive signals G6 andG7 (G5, G8) to the phase of each of the first drive signals G1 and G4(G2, G3), to a set value within a prescribed range, thereby enablingadjustment of the magnitude of the output power. Thus, even when achange in the relative positional relationship between the primary coilL1 and the secondary coil L2 changes the coupling coefficient betweenthe primary coil L1 and the secondary coil L2, adjusting the phasedifference θ enables the non-contact power supply apparatus 2 to easilysecure required electric power. Moreover, since adjusting the phasedifference θ adjusts the output power, the non-contact power supplyapparatus 2 is particularly useful, for example, when the frequency band(allowed frequency band F1) usable as the operation frequency f1 of theinverter circuit 21 is limited. Moreover, since the phase difference θis adjusted to the set value within the prescribed range including atleast one of a range of 270 degrees to 360 degrees and a range of 90degrees to 180 degrees, the inverter circuit 21 is operable in a laggingphase mode when the prescribed range satisfies prescribed conditions.Under the prescribed conditions, the prescribed range in the case of the“initial lagging phase” may be either the range from 270 degrees to 360degrees or the range from 90 degrees to 180 degrees. The prescribedrange in the case of the “initial leading phase” is limited to only therange of 90 degrees to 180 degrees.

Moreover, the prescribed range is preferably the range of 270 degrees to360 degrees. With this configuration, in the case of the “initiallagging phase,” both the inverter circuit 21 and the variablecapacitance circuit 22 is operable in the lagging phase mode when thecontrol circuit 23 adjusts the phase difference θ to the set valuewithin the prescribed range to adjust the magnitude of the output powerof the non-contact power supply apparatus 2.

Alternatively, the prescribed range is preferably a range of 90 degreesto 180 degrees. With this configuration, in the case of the “initialleading phase.” the inverter circuit 21 can be operated in the laggingphase mode when the control circuit 23 adjusts the phase difference θ tothe set value within the prescribed range to adjust the magnitude of theoutput power of the non-contact power supply apparatus 2.

Note that in the non-contact power supply apparatus 2 of the presentembodiment, the prescribed range may be at least one of a range of 270degrees to 360 degrees and a range of 90 degrees to 180 degrees, andlimiting the prescribed range to either one of the ranges is not anessential configuration.

Moreover, as the present embodiment, the control circuit 23 ispreferably configured to adjust the frequencies of the first drivesignals G1 to G4 and the second drive signals G5 to G8 to performfrequency control of adjusting the magnitude of the output power. Inthis case, the control circuit 23 is preferably configured to adjust thephase difference θ to the set value within the prescribed range toadjust the magnitude of the output power when the magnitude of theoutput power after adjustment by the frequency control is less than aprescribed target value. This configuration enables the non-contactpower supply apparatus 2 to adjust the output power in two steps, thefrequency control and the phase difference control, and therefore, it ispossible to set a wide adjustment range of the output power.

Moreover, as the present embodiment, the non-contact power supplyapparatus 2 preferably further includes the meter 24 configured tomeasure the magnitude of a current flowing through the primary coil L1as a measured value. The control circuit 23 preferably has a search modefor estimating a coupling coefficient between the primary coil L1 andthe secondary coil L2. In this case, the control circuit 23 ispreferably configured to gradually cause a change in the phasedifference θ within the prescribed range in the search mode and toestimate the coupling coefficient based on a change in the measuredvalue along with the change in the phase difference θ. Thisconfiguration enables the non-contact power supply apparatus 2 toestimate the coupling coefficient between the primary coil L1 and thesecondary coil L2 and further to estimate the resonance characteristicsand the like from the coupling coefficient. The control circuit 23operates in the search mode before stating operation in the normal modeand can thus set an appropriate value as the initial value of theoperation frequency f1 when the operation in the normal mode is started.

Moreover, as the present embodiment, when the control circuit 23includes a microcomputer as a main component, a program stored in amemory of the microcomputer is a program which causes a computer(microcomputer) to function as a controller (control circuit 23),wherein the computer is used in the non-contact power supply apparatus2. The non-contact power supply apparatus 2 here includes the invertercircuit 21, the primary coil L1, and the variable capacitance circuit22. The controller (control circuit 23) is configured to control theplurality of conversion switching elements Q1 to Q4 by the first drivesignals G1 to G4 and to control the plurality of adjustment switchingelements Q5 to Q8 by the second drive signals G5 to G8. The controller(control circuit 23) is configured to adjust the phase difference θ to aset value within a prescribed range including at least one of a range of270 degrees to 360 degrees and a range of 90 degrees to 180 degrees toadjust the magnitude of the output power.

This program provides advantages that functions equivalent to those ofthe non-contact power supply apparatus 2 of the present embodiment canbe realized even without the control circuit 23 and that even when therelative positional relationship between the primary coil L1 and thesecondary coil L2 changes, required electric power is easily secured.

Moreover, controlling the non-contact power supply apparatus 2 includingthe inverter circuit 21, the primary coil L1, and the variablecapacitance circuit 22 by the following control method enablesrealization of functions equivalent to those of the non-contact powersupply apparatus 2 of the present embodiment even without the controlcircuit 23.

That is, the method for controlling the non-contact power supplyapparatus 2 is a method which includes controlling the plurality ofconversion switching elements Q1 to Q4 by the first drive signals G1 toG4 and controlling the plurality of adjustment switching elements Q5 toQ8 by the second drive signals G5 to G8. In this method, the phasedifference θ is adjusted to a set value within a prescribed rangeincluding at least one of a range of 270 degrees to 360 degrees and arange of 90 degrees to 180 degrees to adjust the magnitude of the outputpower.

The method for controlling the non-contact power supply apparatus 2provides advantages that functions equivalent to those of thenon-contact power supply apparatus 2 of the present embodiment can berealized even without the control circuit 23 and that even when therelative positional relationship between the primary coil L1 and thesecondary coil L2 changes, required electric power is easily secured.

<As to Primary Coil, Secondary Coil>

Here, the primary coil L1 and the secondary coil L2 of the presentembodiment may be solenoid coils each obtained by helically winding aconductor wire onto a core but is preferably spiral coils each obtainedby spirally winding a conductor wire on a flat pane. The spiral coil hasthe advantage that unnecessary interference noise is less likely tooccur as compared to the solenoid coil. Moreover, using the spiral coilreduces the unnecessary interference noise and consequently provides theadvantage of an expanded operation frequency range available to theinverter circuit 21. This point will be described in detail below.

That is, the resonance characteristics of the non-contact powertransmission system 1, as described above, changes depending on thecoupling coefficient of the primary coil L1 and the secondary coil L2,and under a certain condition, as illustrated in FIG. 12, the resonancecharacteristics show so-called double-crest characteristics having twolocal maximum values of an output. As illustrated in FIG. 12, in theresonance characteristics (double-crest characteristics), two “crests”occur at which the output is local maximum with a first frequency fr1and a third frequency fr3. Between these two “crests,” a “trough” isformed at which the output is local minimum with a second frequency fr2.Here, the first frequency fr1, the second frequency fr2, and the thirdfrequency fr3 are in a relationship expressed as fr1<fr2<fr3. In thefollowing description, with reference to the second frequency fr2, afrequency range lower than the second frequency fr2 is referred to as a“low-frequency range,” and a frequency range higher than the secondfrequency fr2 is referred to as a “high-frequency range.”

In such resonance characteristics, each of the “crest” (crest which islocal maximum at the first frequency fr1) of the low-frequency range andthe “crest” (crest which is local maximum at the third frequency fr3) ofthe high-frequency range has a region (hereinafter referred to as a“lagging region”) in which the inverter circuit 21 operates in thelagging phase mode. Thus, the inverter circuit 21 is operable in thelagging phase mode when the operation frequency f1 is assigned to eitherof the two “crests.”

Here, the case where the operation frequency f1 of the inverter circuit21 is assigned to the “crest” of the low-frequency range is comparedwith the case where the operation frequency f1 of the inverter circuit21 is assigned to the “crest” of the high-frequency range. Theunnecessary interference noise in the case where the operation frequencyf1 is assigned to the “crest” of the low-frequency range is smaller thanthat in the case where the operation frequency f1 is assigned to the“crest” of the high-frequency range. That is, at the “crest” of thehigh-frequency range, a current flowing through the primary coil L1 anda current flowing through the secondary coil L2 are in the same phase.In contrast, at the “crest” of the low-frequency range, the currentflowing through the primary coil L1 and the current flowing through thesecondary coil L2 are in an ant-phase. Thus, at the “crest” of thelow-frequency range, the unnecessary interference noise generated at theprimary coil L1 and the unnecessary interference noise generated at thesecondary coil L2 cancel out each other, and therefore, the unnecessaryinterference noise is reduced in the entire non-contact powertransmission system 1.

Thus, even when the solenoid coil is adopted, if the operation frequencyf1 of the inverter circuit 21 is within a lagging region (from the firstfrequency fr1 to the second frequency fr2) of the “crest” of thelow-frequency range, the inverter circuit 21 operates in the laggingphase mode, and the unnecessary interference noise is also reduced.However, the lagging region of the “crest” of the low-frequency rangechanges depending on the coupling coefficient of the primary coil L1 andthe secondary coil L2, and therefore, control for setting the operationfrequency f1 of the inverter circuit 21 within such an indeterminatelagging region is required.

In contrast, in the case of the spiral coil, even when the operationfrequency f1 of the inverter circuit 21 is within a lagging region(frequencies higher than the third frequency fr3) of the “crest” of thehigh-frequency range, the unnecessary interference noise issignificantly reduced as compared to the solenoid coil. That is, the useof the spiral coil does not limit the operation frequency f1 of theinverter circuit 21 to the lagging region of the “crest” of thelow-frequency range but expands the range of the operation frequency f1available to the inverter circuit 21. Note that the lagging region ofthe “crest” of the high-frequency range is also an indeterminate region,but when the operation frequency f1 of the inverter circuit 21 is sweptfrom a sufficiently high frequency toward a low frequency, the operationfrequency f1 passes through the lagging region of the “crest” of thehigh-frequency range, and therefore, no complicated control is required.

<Variation>

The variable capacitance circuit 22 is not limited to the configurationusing the four adjustment switching elements Q5 to Q8 as described inthe present embodiment. The variable capacitance circuit 22 may have aconfiguration including two adjustment switching elements Q9 and Q10 asillustrated in FIG. 13. In a variable capacitance circuit 22 shown inFIG. 13, each of the adjustment switching elements Q9 and Q10 is asemiconductor switching element having a double-gate structure includingtwo gates. Moreover, the first adjustment switching element Q9 iselectrically connected in series to an adjustment capacitor C1. Thesecond adjustment switching element Q10 is electrically connected inparallel to a series circuit of the adjustment switching element Q9 andthe adjustment capacitor C1. The two gates of the adjustment switchingelement Q9 receive respective second drive signals G7 and G8.

Moreover, the two gates of the adjustment switching element Q10 receiverespective second drive signals G5 and G6. In the variable capacitancecircuit 22 shown in FIG. 13, the two adjustment switching elements Q9and Q10 are controlled by the second drive signals G5 to G8, and thevariable capacitance circuit 22 shown in FIG. 13 functions equivalentlyto the variable capacitance circuit 22 shown in FIG. 1.

Moreover, a load to which output power is supplied (i.e., charged) fromthe non-contact power supply apparatus 2 in a non-contact manner is notlimited to an electric vehicle, but may be an electrical deviceincluding a storage battery such as mobile phones and smartphones or anelectrical device including no storage battery such as lightingfixtures.

Moreover, a method for transmitting output power from the non-contactpower supply apparatus 2 to the non-contact power reception apparatus 3is not limited to the above-described magnetic field resonance methodbut may be an electromagnetic induction method, a microwave transmissionmethod, or the like.

Moreover, each of the conversion switching elements Q1 to Q4 and each ofthe adjustment switching elements Q5 to Q8 may include othersemiconductor switching elements such as bipolar transistors. InsulatedGate Bipolar Transistors (IGBTs), and the like.

Moreover, each of the diodes D1 to D4 is not limited the parasitic diodeof each of the conversion switching elements Q1 to Q4 but may beexternally provided to each of the conversion switching elements Q1 toQ4. Similarly, each of the diodes D5 to D8 is not limited to theparasitic diode of each of the adjustment switching elements Q5 to Q8but may be externally provided to each of the adjustment switchingelements Q5 to Q8.

Moreover, the configuration of the meter 24 is not limited to theconfiguration that the meter 24 is provided separately from the controlcircuit 23. The meter 24 may be provided integrally with the controlcircuit 23. Moreover, since it is required only that the meter 24 canmeasure the magnitude of the current flowing through the primary coilL1, the location of the current sensor 25 is not limited between theprimary coil L1 and the second primary capacitor C12 but the currentsensor 25 may be disposed on a path through which a current flowing tothe primary coil L1 flows.

Moreover, it is not essential for the control circuit 23 to performfrequency control, but the control circuit 23 may be configured toadjust the magnitude of the output power by only the phase differencecontrol.

Moreover, the inverter circuit 21 may be a voltage inverter configuredto convert a direct-current voltage into an alternating-current voltageand to be able to output the alternating-current voltage, and theinverter circuit 21 is not limited to the full-bridge inverter circuitincluding full-bridge connection of the four conversion switchingelements Q1 to Q4. The inverter circuit 21 may be, for example, ahalf-bridge inverter circuit.

REFERENCE SIGNS LIST

-   -   1 Non-Contact Power Supply System    -   2 Non-Contact Power Supply Apparatus    -   3 Non-Contact Power Reception Apparatus    -   21 Inverter Circuit    -   211, 212 Pair of Input Points    -   213, 214 Pair of Output Points    -   22 Variable Capacitance Circuit    -   23 Control Circuit (Controller)    -   24 Meter    -   C11 Adjustment Capacitor    -   G1 to G4 First Drive Signal    -   G5 to G8 Second Drive Signal    -   L1 Primary Coil    -   L2 Secondary Coil    -   Q1 to Q4 Conversion Switching Element    -   Q5 to Q8 Adjustment Switching Element    -   Q9, Q10 Adjustment Switching Element    -   θ Phase Difference

1. A non-contact power supply apparatus, comprising: an inverter circuitwhich includes a plurality of conversion switching elements electricallyconnected between a pair of input points and a pair of output points andwhich is configured to convert a direct-current voltage applied to thepair of input points into an alternating-current voltage by switchingthe plurality of conversion switching elements and to output thealternating-current voltage from the pair of output points; a primarycoil electrically connected between the output points in the pair andconfigured to supply output power to a secondary coil in a non-contactmanner when the alternating-current voltage is applied to the primarycoil; a variable capacitance circuit electrically connected between thepair of output points and the primary coil, including an adjustmentcapacitor and a plurality of adjustment switching elements, andconfigured to adjust a magnitude of a capacity component between thepair of output points and the primary coil by switching the plurality ofadjustment switching elements; and a control circuit configured tocontrol the plurality of conversion switching elements by a first drivesignal and to control the plurality of adjustment switching elements bya second drive signal, wherein the control circuit is configured toadjust a phase difference which is a delay of a phase of the seconddrive signal to a phase of the first drive signal to a set value withina prescribed range to operate the inverter circuit in a lagging phasemode and to adjust a magnitude of the output power, and the prescribedrange includes at least one of a range of 270 degrees to 360 degrees anda range of 90 degrees to 180 degrees.
 2. The non-contact power supplyapparatus according to claim 1, wherein the prescribed range is therange of 270 degrees to 360 degrees.
 3. The non-contact power supplyapparatus according to claim 1, wherein the prescribed range is therange of 90 degrees to 180 degrees.
 4. The non-contact power supplyapparatus according to claim 1, wherein the control circuit isconfigured to adjust frequencies of the first drive signal and thesecond drive signal to perform frequency control of adjusting themagnitude of the output power, and the control circuit is configured toadjust the phase difference to the set value within the prescribed rangeto adjust the magnitude of the output power when the magnitude of theoutput power after adjustment by the frequency control is less than aprescribed target value.
 5. The non-contact power supply apparatusaccording to claim 1, further comprising: a meter configured to measurea magnitude of a current flowing through the primary coil as a measuredvalue, wherein the control circuit has a search mode for estimating acoupling coefficient between the primary coil and the secondary coil,and the control circuit is configured to gradually cause a change in thephase difference within the prescribed range in the search mode and toestimate the coupling coefficient based on a change in the measuredvalue along with the change in the phase difference.
 6. A non-transitorycomputer-readable recording medium recording a program which causes acomputer to function as a controller, wherein the computer is used in anon-contact power supply apparatus including: an inverter circuit whichincludes a plurality of conversion switching elements electricallyconnected between a pair of input points and a pair of output points andwhich is configured to convert a direct-current voltage applied to thepair of input points into an alternating-current voltage by switchingthe plurality of conversion switching elements and to output thealternating-current voltage from the pair of output points; a primarycoil electrically connected between the output points in the pair andconfigured to supply output power to a secondary coil in a non-contactmanner when the alternating-current voltage is applied to the primarycoil; and a variable capacitance circuit electrically connected betweenthe pair of output points and the primary coil, including an adjustmentcapacitor and a plurality of adjustment switching elements, andconfigured to adjust a magnitude of a capacity component between thepair of output points and the primary coil by switching the plurality ofadjustment switching elements, and the controller is configured tocontrol the plurality of conversion switching elements by a first drivesignal, to control the plurality of adjustment switching elements by asecond drive signal, to adjust a phase difference which is a delay of aphase of the second drive signal to a phase of the first drive signal toa set value within a prescribed range including at least one of a rangeof 270 degrees to 360 degrees and a range of 90 degrees to 180 degreesto operate the inverter circuit in a lagging phase mode and to adjust amagnitude of the output power.
 7. A method for controlling a non-contactpower supply apparatus including: an inverter circuit which includes aplurality of conversion switching elements electrically connectedbetween a pair of input points and a pair of output points and which isconfigured to convert a direct-current voltage applied to the pair ofinput points into an alternating-current voltage by switching theplurality of conversion switching elements and to output thealternating-current voltage from the pair of output points; a primarycoil electrically connected between the output points in the pair andconfigured to supply output power to a secondary coil in a non-contactmanner when the alternating-current voltage is applied to the primarycoil; and a variable capacitance circuit electrically connected betweenthe pair of output points and the primary coil, including an adjustmentcapacitor and a plurality of adjustment switching elements, andconfigured to adjust a magnitude of a capacity component between thepair of output points and the primary coil by switching the plurality ofadjustment switching elements, the method comprising: controlling theplurality of conversion switching elements by a first drive signal,controlling the plurality of adjustment switching elements by a seconddrive signal, and adjusting a phase difference which is a delay of aphase of the second drive signal to a phase of the first drive signal toa set value within a prescribed range including at least one of a rangeof 270 degrees to 360 degrees and a range of 90 degrees to 180 degreesto operate the inverter circuit in a lagging phase mode and to adjust amagnitude of the output power.
 8. A non-contact power transmissionsystem, comprising: the non-contact power supply apparatus accordingclaim 1; and a non-contact power reception apparatus including thesecondary coil, wherein the non-contact power reception apparatus isconfigured to be supplied with the output power from the non-contactpower supply apparatus in a non-contact manner.
 9. The non-contact powersupply apparatus according to claim 2, wherein the control circuit isconfigured to adjust frequencies of the first drive signal and thesecond drive signal to perform frequency control of adjusting themagnitude of the output power, and the control circuit is configured toadjust the phase difference to the set value within the prescribed rangeto adjust the magnitude of the output power when the magnitude of theoutput power after adjustment by the frequency control is less than aprescribed target value.
 10. The non-contact power supply apparatusaccording to claim 3, wherein the control circuit is configured toadjust frequencies of the first drive signal and the second drive signalto perform frequency control of adjusting the magnitude of the outputpower, and the control circuit is configured to adjust the phasedifference to the set value within the prescribed range to adjust themagnitude of the output power when the magnitude of the output powerafter adjustment by the frequency control is less than a prescribedtarget value.
 11. The non-contact power supply apparatus according toclaim 2, further comprising: a meter configured to measure a magnitudeof a current flowing through the primary coil as a measured value,wherein the control circuit has a search mode for estimating a couplingcoefficient between the primary coil and the secondary coil, and thecontrol circuit is configured to gradually cause a change in the phasedifference within the prescribed range in the search mode and toestimate the coupling coefficient based on a change in the measuredvalue along with the change in the phase difference.
 12. The non-contactpower supply apparatus according to claim 3, further comprising: a meterconfigured to measure a magnitude of a current flowing through theprimary coil as a measured value, wherein the control circuit has asearch mode for estimating a coupling coefficient between the primarycoil and the secondary coil, and the control circuit is configured togradually cause a change in the phase difference within the prescribedrange in the search mode and to estimate the coupling coefficient basedon a change in the measured value along with the change in the phasedifference.
 13. The non-contact power supply apparatus according toclaim 4, further comprising: a meter configured to measure a magnitudeof a current flowing through the primary coil as a measured value,wherein the control circuit has a search mode for estimating a couplingcoefficient between the primary coil and the secondary coil, and thecontrol circuit is configured to gradually cause a change in the phasedifference within the prescribed range in the search mode and toestimate the coupling coefficient based on a change in the measuredvalue along with the change in the phase difference.
 14. The non-contactpower supply apparatus according to claim 9, further comprising: a meterconfigured to measure a magnitude of a current flowing through theprimary coil as a measured value, wherein the control circuit has asearch mode for estimating a coupling coefficient between the primarycoil and the secondary coil, and the control circuit is configured togradually cause a change in the phase difference within the prescribedrange in the search mode and to estimate the coupling coefficient basedon a change in the measured value along with the change in the phasedifference.
 15. The non-contact power supply apparatus according toclaim 10, further comprising: a meter configured to measure a magnitudeof a current flowing through the primary coil as a measured value,wherein the control circuit has a search mode for estimating a couplingcoefficient between the primary coil and the secondary coil, and thecontrol circuit is configured to gradually cause a change in the phasedifference within the prescribed range in the search mode and toestimate the coupling coefficient based on a change in the measuredvalue along with the change in the phase difference.